Loblolly pine chips were treated with several white-rot fungi in two different bioreactor configurations for four weeks prior to refiner mechanical pulping. Irrespective of the bioreactor configuration, all fungal treatments caused some chip weight loss and saved electrical energy during fiberization and refining as compared to the untreated control. Some of the fungal treatments improved strength properties of the handsheets, whereas brightness and light scattering coefficient of the handsheets were decreased after all of the fungal treatments. Opacity of the handsheets after the fungal treatments remained unchanged. Based on energy savings and improvements in the strength properties, regardless of bioreactor type, the white-rot fungus Ceriporiopsis subvermispora appeared to be superior to the other white-rot fungi tested. When incubated in stationary tray bioreactors, C. subvermispora caused only 6% weight loss, saved 42% energy during fiberization and refining, improved burst index by 32% and tear index by 67%, as compared to the control.

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These small-diameter pulps were compared with commercially obtained sawmill residue chips of a Douglasfir/western larch mixture and lodgepole pine. These pulps were also evaluated to see if CTMP improved the properties of the final product compared with products made using TMP. Compared with the controls, the CTMP prepared from Douglas-fir and lodgepole pine small trees and Douglas-fir submerchantable logs consumed more electrical energy during pulp preparation and had higher paper strength properties and lower optical properties. Also compared with the controls, lodgepole pine submerchantable logs consumed about the same electrical energy and had marginal strength properties and higher optical properties. Western larch submerchantable logs and small trees had the lowest electrical energy consumption of all pulps tested, low strength properties, but some of the higher optical properties. Western larch submerchantable logs and small trees appear to be unsuitable for CTMP. For the majority of the materials, CTMP improved the properties of the final product compared with corresponding TMP. To restore and maintain forest ecosystem health and function in the western interior of the United States, many smalldiameter stems need to be removed from densely stocked stands. In general, these materials are underutilized. Information on the properties of these resources is needed to help forest managers understand when timber sales are a viable option to accomplish ecosystem management objectives. Providing proof that this small-diameter material yields quality pulp would help increase its value and therefore help remove it from the forest. This study examines the acceptability of the small-diameter resource as a raw material for high-yield chemithermomechanical pulping (CTMP), which has the potential for improved fiber characteristics and paper strength compared with those of thermomechanical pulping (TMP). Pulps using CTMP were prepared from lodgepole pine and mixed Douglasfir/western larch sawmill residue chips; lodgepole pine, Douglas-fir, and western larch submerchantable logs; and lodgepole pine, Douglas-fir, and western larch small trees.

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